A technique for a vehicle to detect an obstacle approaching the surroundings of the vehicle by using an obstacle sensor mounted on the vehicle has heretofore been known.
For example, in Japanese Patent Application Publication No. 2009-280109, a rear portion of the vehicle is mounted with an ultrasonic sensor having a detection region rearward of the vehicle, and an ultrasonic sensor having a detection region laterally rearward of the vehicle. The ultrasonic sensor having the detection region laterally rearward of the vehicle has a detectable region in which an obstacle located even far away in the rear is detectable, whereas the ultrasonic sensor having the detection region rearward of the vehicle can detect the obstacle only in the vicinity of the vehicle. Therefore, an undetectable region in which any obstacle is undetectable is present far away right behind the vehicle.